1. Field of the Invention
This invention relates to the removal of acid-soluble substances from various media, and particularly to foam treating fluids useful for contacting permeable or impervious media to dissolve a portion of the media surfaces or materials deposited therein or thereon to increase the permeability of the media, or to clean the media, and more particularly useful for dissolving acid-soluble portions of a subterranean geological reservoir, acid-soluble materials previously deposited in the reservoir or a well and, in some embodiments, also of dissolving organic materials present in the reservoir or a well, as well as dissolving scale from an industrial vessel or conduit.
2. Description of the Art
It has long been known to contact various solid media with a treating fluid capable of dissolving portions of the media or materials present in or on the surface. If a medium is permeable, such as a subterranean reservoir or a screen in a well, the treating fluid can increase the permeability therethrough. If a medium is impermeable, such as an industrial vessel or conduit, the treating fluid cleans the surface. Typical of such treating solutions is an aqueous solution of a mineral acid capable of dissolving carbonates present in a reservoir or scale and other inorganic materials previously deposited in the reservoir or vessel by fluids flowing therethrough. It is also known to remove from such media organic materials such as paraffins, viscous oil, tar, wax, asphaltenes, and resin precipitates of petroleum origin, by contacting the media with a treating fluid containing both a water-soluble acid component and an oil-soluble organic solvent, such as crude oil or a fraction thereof. Such treating fluids typically also contain a surface active agent and are in emulsion or dispersed form. Such emulsions or dispersions are often relatively easy to form with any one of a number of anionic, cationic, nonionic, or amphoteric foaming agents.
In order to minimize the liquid volume of treating fluid required for a given treatment and decrease the density of the treating fluid, it is known to add to a liquid treating fluid a foaming agent and a gas to form a relatively large volume of foamed treating fluid.
U.S. Pat. No. 3,572,440 to Hutchison et al. discloses a preformed well circulation foam containing water, a mineral acid or lower organic acid component, a gas and an organic foaming agent. Suitable foaming agents are anionic (preferred), cationic, nonionic and amphoteric agents. Mixtures of two or more foaming agent species are contemplated and a mixture of alkylbenzene sulfonic acids and alpha-olefin sulfonic acids is preferred.
Certain cationic quaternary ammonium compounds have been suggested for use in well-acidizing compositions for purposes other than forming a foam.
U.S. Pat. No. 3,932,296 to Byth describes a corrosion inhibitor for hydrochloric acid used in acidizing formations which inhibitor is a mixture of (1) the reaction product of a particular nitrogen compound such as an alkyl amine, an aldehyde, a fatty acid and a first quaternary ammonium compound, and (2) a second quaternary ammonium compound which is different from the first such compound.
U.S. Pat. No. 4,201,678 to Pye et al. describes an aqueous foam drilling fluid for high temperature reservoirs employing as a foaming agent a mixture of an amphoteric betaine and a salt of a linear aliphatic or alkyl aryl hydrocarbon sulfonate. Neither acid nor solvent is used in the drilling fluid.
Foams containing only water, an acid component, and a gas are relatively easy to form. Any one of a wide variety of types of foaming agents can be used. When an organic solvent component and an emulsifying agent are also employed in the composition and the resulting emulsion or dispersion foamed, the foam is more difficult to form and a more effective and different foaming agent is often required. Also, it is common practice in many instances to employ either type of foam under conditions adverse to its stability, e.g., pumping it several thousand feet down a well and into the surrounding reservoir which is at an elevated temperature and pressure, contacting the foam with crude oil and/or aqueous solutions containing calcium chloride, and the like, or introducing it into a vessel or conduit at elevated temperature and/or pressure. Such conditions require that an especially effective foaming agent be used if the foam is to remain stable long enough for the treatment to be completed. In many foamed treating agent compositions containing an acid component, various other additives are employed to impart a number of attributes to the fluid. Such additives are often adverse to foam stability. Examples of such additives include corrosion inhibitors, antisludge agents, and emulsifying agents, commonly used in well-acidizing treating treating fluids. When an acid-containing foamed treating agent dissolves components of a scale or formation rock, the dissolved components sometimes decrease foam stability.
While each of the aforementioned compositions has met with some success in particular applications, the need exists for a further improved foamed treating fluid composition and method.
Accordingly, a principal object of this invention is to provide a composition and method for forming a stable foamed treating fluid containing an acid component.
Another object of this invention is to provide such a composition which also contains organic solvent and emulsifying agent components.
Yet another object of this invention is to provide such a composition which remains stable and effective even though it contains or becomes admixed with or dissolves additives or contaminants which are adverse to the stability of the foam.
A further object of this invention is to provide a method for using a foam treating fluid in treating subterranean reservoirs or wells or cleaning industrial vessels or conduits.
Other objects, advantages and features of this invention will become apparent to those skilled in the art from the following description and appended claims.